Commit d206121f authored by Alexander Lobakin's avatar Alexander Lobakin Committed by David S. Miller
Browse files

skbuff: micro-optimize {,__}skb_header_pointer() 



{,__}skb_header_pointer() helpers exist mainly for preventing
accesses-beyond-end of the linear data.
In the vast majorify of cases, they bail out on the first condition.
All code going after is mostly a fallback.
Mark the most common branch as 'likely' one to move it in-line.
Also, skb_copy_bits() can return negative values only when the input
arguments are invalid, e.g. offset is greater than skb->len. It can
be safely marked as 'unlikely' branch, assuming that hotpath code
provides sane input to not fail here.

These two bump the throughput with a single Flow Dissector pass on
every packet (e.g. with RPS or driver that uses eth_get_headlen())
on 20 Mbps per flow/core.

Signed-off-by: default avatarAlexander Lobakin <alobakin@pm.me>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 59753ce8

include/linux/skbuff.h

+2 −3
Original line number Diff line number Diff line
@@ -3680,11 +3680,10 @@ static inline void * __must_check 
__skb_header_pointer(const struct sk_buff *skb, int offset, int len,

		     const void *data, int hlen, void *buffer)

{

	if (hlen - offset >= len)

	if (likely(hlen - offset >= len))

		return (void *)data + offset;



	if (!skb ||

	    skb_copy_bits(skb, offset, buffer, len) < 0)

	if (!skb || unlikely(skb_copy_bits(skb, offset, buffer, len) < 0))

		return NULL;



	return buffer;